Government Code and Cypher School: Signals Intelligence Passed to the Prime Minister, Messages and Correspondence

A file of signals intelligence reports, messages, and correspondence issued by the Government Code and Cypher School and sent by the head ('C') of the Secret Intelligence Service (MI6) to the Prime Minister, Winston Churchill. This file contains a minute from C to the Prime Minister (PM) covering 11 summaries of naval messages, 887, 892, 896, 906, 909, 912, 920, 921, 922, 924, 925 (all not included); C adds a manuscript note that SHARK had been exploitable since the PM's departure.